Conventionally, the filtering cartridge is held or restrained in terms of longitudinal movement inside the outer shell at the one end with the filter head and at the other end by an end wall of the outer shell.
This type of filter operates in the following manner: The fluid to be filtered (for example, oil) is introduced through an intake opening of the filter head, to an annular chamber in the outer shell, flows along the internal wall of the outer shell, and passes radially inward through the filtering cartridge, which retains the contaminants (particularly particles of heavy metals) found in suspension in the fluid. The filtered fluid then passes through the central axis of the outer shell and leaves through an outlet opening of the head.
When the filtering cartridge placed in the outer shell reaches the end of its useable life, that is to say when the filtering cartridge no longer satisfactorily fulfills its role of filtration, an operator separates the outer shell from the filter head, removes the worn out filtering cartridge, replaces it with a new filtering cartridge, and reattaches the outer shell to the filter head. Used filtering cartridges are subsequently incinerated so as to destroy the organic polluting materials and to concentrate the inorganic polluting materials (particularly the heavy metals, such as lead).
This type of filter, however, offers several disadvantages. A first disadvantage lies in the fact that the used filtering cartridge cannot be completely incinerated because it generally contain certain metallic elements, particularly end plates and a central perforated interior tube. The elimination of this remaining waste is made more complicated at the expense of the environment.
Another disadvantage is connected with the longitudinal restraining of the filtering cartridge inside the outer shell. In effect, this restraining requires one to take into account precisely the relative positioning of the outer shell with respect to the filter head since the outer shell serves as a lower stop for one end of the filtering cartridge. In other words, the longitudinal play of the filtering cartridge in the outer shell depends on the dimensioning of the outer shell.
Finally, the shape of this type of filter is such that it has a certain number of interfaces or joints where fluid leakage could occur. It therefore requires the use of several seals.